A rotating annulus driven by localized convective forcing: a new atmosphere-like experiment

Abstract

unstable flows which are qualitatively similar to those previously observed in the classical thermally driven annulus. However, in contrast to the classical configuration, they typically exhibit more spatio-temporal complexity. Thus, several regimes of flow demonstrate the equilibrated coexistence of, and interaction between, free convection and baroclinic wave modes. These new features were not previously observed in the classical annulus and validate the new setup as a tool for exploring fundamental atmosphere-like dynamics in a more realistic framework. Thermal structure in the fluid is investigated and found to be qualitatively consistent with previous numerical results, with nearly isothermal conditions, respectively, above and below the heat source and sink, and stably-stratified, sloping isotherms in the near-adiabatic interior.

Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing

“…Sandwiched between these two convective zones is a baroclinic region with approximately uniformly sloping isotherms. This thermal structure has also been observed in experiment as shown by Scolan and Read [18] (Figure 6 of that paper). As before, prograde azimuthal velocity is seen close to the top of the tank and retrograde motion near the bottom with the most intense movement occuring at small radii.…”

“…To reduce any effect of fluctuations in the Nusselt number across the domain, the Nusselt number used here is taken to be the mean of the Nusselt number over the heat sink and that over the heat source. The numerical simulations carried out were configured to emulate the setup of the laboratory experiment [18]. The fluid is contained between two upright, rigid, coaxial cylinders and a flat horizontal base.…”

“…With a view to making comparisons with future data from the laboratory experiment, the simulations will be run using the same dimensions and system properties as the laboratory experiment, for example the same Prandtl number and density for the working fluid. Preliminary experimental results are presented by Scolan and Read [18]. The numerical simulations are carried out for axisymmetric circulations over a wide range of control parameters.…”

“…Due to the heating of the atmosphere by re-emission from the surface and cooling at high altitudes a more realistic analogue to a planetary atmosphere is to heat the annulus through the bottom surface and cool it at the top. A new annulus experiment is currently undergoing construction in the Atmospheric, Oceanic and Planetary Physics laboratory in Oxford within which top cooling and bottom heating will be used [18]. The cooling takes place in a narrow ring around the central cylinder whilst the fluid is heated through a ring covering the outermost radii.…”

“…Close to the bottom of the tank at small radii retrograde motion begins to develop. Using streaklines to visualise the flow, Scolan and Read [18] showed that for weak rotation the flow in the experiment remains approximately axisymmetric. 3.…”